Appeal to Tradition is a fallacy that occurs when it is assumed that something is better or correct simply because it is older, traditional, or "always has been done." This sort of
"reasoning" has the following form:

X is old or traditional

Therefore X is correct or better.

This sort of "reasoning" is fallacious because the age of something does not automatically make it correct or better than something newer. This is made quite obvious by the following example:
The theory that witches and demons cause disease is far older than the theory that microrganisms cause diseases. Therefore, the theory about witches and demons must be true.

This sort of "reasoning" is appealing for a variety of reasons. First, people often prefer to stick with what is older or traditional. This is a fairly common psychological characteristic of people which may stem from the fact that people feel more comfortable about what has been around longer. Second, sticking with things that are older or traditional is often easier than testing new things. Hence, people often prefer older and traditional things out of laziness. Hence, Appeal to Tradition is a somewhat common fallacy.

It should not be assumed that new things must be better than old things (see the fallacy Appeal to Novelty) any more than it should be assumed that old things are better than new things. The age of something does not, in general, have any bearing on its quality or correctness (in this context). In the case of tradition, assuming that something is correct just because it is considered a tradition is poor reasoning. For example, if the belief that 1+1 = 56 were a tradition of a group of people it would hardly follow that it is true.

Obviously, age does have a bearing in some contexts. For example, if a person concluded that aged wine would be better than brand new wine, he would not be committing an Appeal to Tradition. This is because, in such cases the age of the thing is relevant to its quality. Thus, the fallacy is committed only when the age is not, in and of itself, relevant to the claim.

One final issue that must be considered is the "test of time." In some cases people might be assuming that because something has lasted as a tradition or has been around a long time that it is true because it has "passed the test of time." If a person assumes that something must be correct or true simply because it has persisted a long time, then he has committed an Appeal to Tradition. After all, as history has shown people can persist in accepting false claims for centuries.

However, if a person argues that the claim or thing in question has successfully stood up to challenges and tests for a long period of time then they would not be committing a fallacy. In such cases the claim would be backed by evidence. As an example, the theory that matter is made of subatomic particles has survived numerous tests and challenges over the years so there is a weight of evidence in its favor. The claim is reasonable to accept because of the weight of this evidence and not because the claim is old. Thus, a claim’s surviving legitimate challenges and passing valid tests for a long period of time can justify the acceptance of a claim. But mere age or persistence does not warrant accepting a claim.

Sure I believe in God. People have believed in God for thousands of years so it seems clear that God must exist. After all, why else would the belief last so long?

Gunthar is the father of Connan. They live on a small island and in their culture women are treated as property to be exchanged at will by men.

Connan: "You know father, when I was going to school in the United States I saw that American women are not treated as property. In fact, I read a book by this person named Mill in which he argued for women’s rights."

Gunthar: "So, what is your point son?"

Connan: "Well, I think that it might be wrong to trade my sisters for cattle. They are human beings and should have a right to be masters of their own fate."

Gunthar: "What a strange and new-fangled notion you picked up in America. That country must be even more barbaric then I imagined. Now think about this son. We have been trading women for cattle for as long as our people have lived on this island. It is a tradition that goes back into the mists of time. "

Connan: "But I still think there is something wrong with it."

Gunthar: "Nonsense my boy. A tradition this old must be endorsed by the gods and must be right."

Of course this mode of government is the best. We have had this government for over 200 years and no one has talked about changing it in all that time. So, it has got to be good.

A reporter is interviewing the head of a family that has been involved with a feud with another family.

Reporter: "Mr. Hatfield, why are you still fighting it out with the Mcoys?"

Hatfield: "Well you see young man, my father feuded with the Mcoys and his father feuded with them and so did my great grandfather."

Reporter: "But why? What started all this?"

Hatfield: "I don’t rightly know. I’m sure it was the Mcoys who started it all, though."

Hatfield: "Stop? What are you crazy? This feud has been going on for generations so I’m sure there is a darn good reason why it started. So I aim to keep it going. It has got to be the right thing to do. Hand me my shooting iron boy, I see one of those Mcoy skunks sneaking in the cornfield."